1. Field of the Invention
The present invention relates to image forming apparatuses of the electro-photographic type, and in particular, to fixing devices that fix toner images.
2. Description of Related Art
In fixing devices of image forming apparatuses of the electro-photographic type, as a section for separating the recording material from the fixing member after fixing, there are those that use separation claws and those that use air separating section. As an example of such separating section, in Unexamined Japanese Utility Model Application Publication No. Sho 63 (1988)-140571 it has been proposed that not only the recording material is separated from the fixing member using a first separating section, but also a second separating section that aids the separation by the first separating section. An air separating section is used as the second separating section.
In the separation using a separation claw, there are problems such as the fixing member being scratched by the separation claw, etc. Even if a separation using air is used in combination as in Unexamined Japanese Utility Model Application Publication No. Sho 63 (1988)-140571, it is difficult to prevent the fixing member from getting scratched by the separation claw.
Because of this, the present inventors carried out investigations of the air separating section that separates a recording material from a fixing member by blowing air at the fixing member.
When separation using an air separating section was made, although good separation was made of recording material having a thicknesses more than common sheets such as printing paper or copying paper, the following problems occurred in the case of thin sheets with a basis weight of 60 g/m2 or less.
When separating a recording material from a fixing member using an air separating section, during the separation of recording material with low rigidity such as thin sheets, it becomes necessary to increase the pressure of the air that is blown towards the fixing member. However, it becomes easy for the recording sheet that has been separated from the fixing member using a high pressure air blast to be pressed towards the pressure member side and get adhered to the pressure member. It was possible to avoid the adhering to the pressure member by providing a separation claw on the side of the pressure member. In this manner, by separating the recording sheet from the fixing member using an air separating section, and separating the recording sheet from the pressure member using a separation claw, it becomes possible to separate a thin sheet definitely from both the fixing member and the pressure member and to convey it smoothly inside the fixing device.
However, when a separation claw is provided on the side of the pressure member, it was found that string shaped undulations are formed on the recording material by the separation claw thereby lowering the quality of the copy or printed matter. The string shaped undulations, in addition, have a bad effect on the conveying of the recording material inside a finishing apparatus connected to the image forming apparatus.
The string shaped undulations are explained using FIG. 1.
In FIG. 1, the white part indicates the ridge parts PA, and the hatched part indicates the valley parts PB.
The ridge part indicated by PA is the part of the recording material P that has passed a separation claw 77, and the valley part indicated by PB is the part of the recording material P that has passed between a separation claw 77 and a separation claw 77.
The recording sheet P passes over the position of a separation claw 77 while being pushed by air. Therefore, in the gap formed between a plurality of separation claws 77, the recording sheet P is pushed to a position that is lower than the separation claws 77. As a result, a high-low difference is created between the position of a separation claw 77 and the position of the gap between separation claws 77, and hence string shaped undulations are formed in the recording sheet P as is shown in FIG. 1.
The string shaped undulations of the recording sheet P formed in this manner result in lowering the quality of the printed matter in which images have been formed. Further, when a finishing apparatus has been connected to the image forming apparatus, the conveying inside a finishing apparatus connected to the image forming apparatus of the recording material in which the string shaped undulations shown in FIG. 1 is not carried out smoothly, and it becomes easy for conveying defects to occur such as jamming, etc.